If optical fibers are used as signal transmission cable, data transmission between information equipments, data transmission between industrial equipments, connection between audio equipments, communication in trunk lines and branch lines, and the like are possible.
Optical fiber transmission can speed up electro-optical modulation with simple circuits and increase transmission capacity. Furthermore, optical fiber transmission has such features as being able to reduce generation of electromagnetic noise and resistant to the influence of electromagnetic noise.
In the case of a short haul transmission, plastic optical fibers, plastic cladding silica fibers, and the like can be used. In the plastic optical fiber, both the core and the cladding are made of plastic. The transmission loss of the plastic optical fiber is minimized in the wavelength range near generally 650 nm. On the other hand, in the plastic cladding silica fiber, the core is made of quartz glass, and the cladding is made of plastic. The transmission loss of the plastic cladding silica fiber is minimized in the wavelength range near generally 800 nm. To use each optical fiber near the minimum transmission loss, the light emitting layers need to be made of different materials to vary the emission wavelength.
In this context, as the conductivity type of the substrate of the light emitting device, both p-type and n-type are often used. Furthermore, use of a driver IC for rapid modulation in the light emitting device facilitates reducing noise and downsizing the module. However, if the shape of the lead frame is changed to support the substrates of light emitting devices having different conductivity types, the number of models of packaging members increases undesirably.